1. Field of the Invention
This invention relates to a camera apparatus consisting of a camera body and a lens system which is detachably attached to the camera body and more particularly to a control device for controlling a plurality of driving means including driving means for automatic focus adjustment, driving means for zooming, driving means for automatic exposure adjustment, etc., which are disposed on the side of the lens system.
2. Description of the Related Art
In order to provide a video camera or the like with an automatic focusing (hereinafter referred to as AF), a power zooming (hereinafter referred to as PZ) and an automatic exposure adjustment (hereinafter referred to as AE) function, the conventional video camera has been arranged as follows: With respect to the AF function, the details of speed control over driving means (for shifting a focusing lens group) are determined according to the various characteristics of the photo-taking lens mounted on the camera, such as a focal length f (mm) and an aperture value F in such a manner as to obtain an adequate distance measuring performance. As for the AE function, the details of optimum driving control are determined in such a way as to preclude hunting of a diaphragm in the neighborhood of an apposite aperture value. As regards the PZ function, the camera is arranged to give the advantage of selecting an optimum angle of view.
However, in the event of a camera system permitting the use of interchangeable lenses, the above-stated control must be applicable to a plurality of lenses. The control must be performed appositely to the characteristics such as the zoom ratio, the focal length and the full aperture F-number of each of these lenses. Otherwise, there would arise the following problems:
With respect to the AF function: An AF action either very much delays before attainment of an in-focus state or cannot be stably accomplished because of continuous hunting of a focusing lens group occurring near an in-focus position.
With respect to the AE function: An AE action, like the AF action, either very much delays before attainment of an apposite exposure or cannot be stably performed because of continuous hunting occurring near an aperture value required for the apposite exposure.
With respect to the PZ function: The effect of natural variations in angle of view cannot be obtained.
In a conceivable solution of these problems, driving speeds are specified in some suitable form for the driving means as criteria to be observed within a lens-interchangeable system. With the speeds thus specified in common for the driving means of lenses, it would enable the camera to adequately perform driving control over a plurality of lenses of different characteristics.
With regard to AF driving means, as applied to an interchangeable lens, the following describes the above-stated speed control method. The speed criterion is assumed to be specified as follows: Under a condition where the varying degree .DELTA.Z mm of a circle of confusion occurring when the focusing lens of the lens system is shifted .DELTA.A mm becomes a maximum value (this condition occurs at the longest focal length, i.e., a telephoto end, and at the full aperture in the case of a zoom lens consisting of four lens groups in general), the varying degree .DELTA.Z mm resulting from the shift of lens .DELTA.A mm can be made unvarying by the driving speed for a given period of time t sec. Assuming that the focal length at the telephoto end is fT mm, a degree of position sensitivity of a focusing lens group is So and a full aperture F-number is Fo, the above-stated relation can be expressed as .DELTA.Z=So.times..DELTA.A/Fo. Therefore, in order to make the value .DELTA.Z unvarying by determining the speed for each lens in accordance with the above-stated specified criteria, the value .DELTA.A mm varies with the lens in use. A method of using the above-stated value .DELTA.Z as a speed determining criterion is disclosed in U.S. patent application Ser. No. 385,306 filed on Jul. 25, 1989.
The prior art method described above is theoretically capable of enabling each of the AF, AE and PZ actions to be approximately uniformly accomplished for all the lenses of different characteristics. In actually arranging the lenses, however, the method presents various problems including the difficulty of driving at all the prescribed speeds due to the limited dynamic ranges of the driving means; the necessity of use of expensive driving means capable of coping with a wide range of speeds including some speeds that are not actually used; and the necessity of use of a complex control circuit.